A conventional mixed mode integrated circuit system frequently uses different voltage supplies. Analog signal processing, such as amplification, comparison, impulsive generation, may be performed at high voltage. A flash memory applies an erase signal, a programming signal and a read signal to flash memory cells. The erase signal, programming signal, and read signal have voltage levels greater than a supply voltage. Also in multilevel volatile memories, the variation of the voltage level of the signal falls in a smaller range for the multi-bits signals stored in the memory cells. A charge pump and a voltage regulator may be used to generate the erase signal, the programming signal, and the read signal. Flash memory cells have a select gate, a top gate and a floating gate for charge storage in response to the erase signal, the programming signal and the read signal.